1. Field of the invention
This invention relates to dicarboxylic acid adducts of lignin. More particularly, this invention relates to adducts of lignin and a salt of epoxysuccinate.
Lignin which is employed in the present invention is a complex naturally-occurring solid polymer comprising a group of closely related compounds. The major commercial source of lignin is from the wood pulping industry. The structures of commercial lignin materials vary according to their isolation method and their source. The lignin varies according to its source, such as tree or plant source, and to the treatment it underwent to be separated from cellulose.
2. The Prior Art
Numerous modifications have been made to lignin in order to improve certain properties, such as dispersing ability, flocculating ability, flame retardancy, thermoplasticity, tanning properties and the like.
Although lignin derivatives with improved properties have been prepared by treatment of alkali lignin, none of these derivatives has proven to have as great effectiveness in both dispersing and metal complexing properties as is desirable. This is particularly true with regard to calcium sequestering capacity of lignin. However, polycarboxylic compounds with certain structural configurations are known to be good calcium sequestrants and have been widely used in detergent building and other applications. Among them, the most important are citric acid, ethylenediaminotetraacetic acid (EDTA) and nitrilotriacetic acid (NTA). A general structural feature of these compounds is that the polycarboxylic groups in a molecule are coupled with an electron-rich element, such as oxygen or nitrogen, in the manner expressed by the formula ##EQU1## wherein R.sub.1, R.sub.2 = hydrogen, alkyl or aliphatic carboxylic group; and X = oxygen or nitrogen.
The invention described herein is a lignin adduct which satisfies the above structural requirement for a molecule to be an effective calcium sequestrant. By virtue of its carboxylic nature and water solubility, the product is particularly useful as a dispersant and oil-in-water emulsifier.
It is, therefore, the general object of this invention to provide a lignin dicarboxylic acid.
Another object of this invention is to provide a lignin-derived metal complexing agent, in particular, for calcium.
A further object of this invention is to provide a water-soluble lignocarboxylate useful as a dispersant.
Other objects, features and advantages of this invention will be evident from the following detailed description.